The present invention relates to a hybrid car provided with an electric motor used to drive the vehicle and an internal combustion engine for power generation, and more particularly, to an operating method for a hybrid car, which permits an increased cruising range and improved power performances of the vehicle, without abandoning an advantage of an electric car that the exhaust gas characteristics are excellent.
Recently, the regulations on exhaust gas from those vehicles which use an internal combustion engine as their drive source have been made more rigorous to tackle environmental pollution. In this respect, various new technologies have been developed. Electric cars, which use an electric motor as their drive source and produce no exhaust gas, should be ideal motor vehicles for reduction of the exhaust gas amount. Typical electric cars are designed so that a battery is used to supply the electric motor with electric power. Naturally, however, the available battery capacity for each vehicle is limited, so that the power performances are poorer and the cruising range is shorter than those of the vehicles which use an internal combustion engine as the drive source. In order to make the electric cars more popular, these technical problems are expected to be solved.
Hybrid cars, which are equipped with an electric motor for vehicle drive and an internal combustion engine for power generation, are believed to be promising modern electric ears which can enjoy an increased cruising range. In hybrid cars, a driving current, with which a required motor output determined according to vehicle operating conditions can be produced, is supplied to the electric motor to obtain required power performance. When the storage amount of the battery is reduced, a generator is driven by the engine to charge the battery with the power generated by the generator; and when the battery charging is unnecessary, the engine is stopped.
However, in the case where the engine is operated or stopped depending upon the presence/absence off the need of battery charging, it is in actuality difficult to always produce a required motor output with accuracy even if the electric motor is supplied with a driving current such that the required motor output can be produced. In general, the voltage of power generated by the generator is higher than the output voltage of the battery, and the voltage applied to the motor is higher during operation of the engine than during stoppage of the same. Thus, even if the driving current supplied to the motor is maintained at a constant value, the actual motor output is greater during operation of the engine than during stoppage of the same. Accordingly, even when the vehicle operating condition remains unchanged and the motor output must be maintained at a constant level, the actual motor output varies and also the running characteristics of the vehicle vary, depending on whether the engine is operating or stopped. Likewise, also when the vehicle operating condition changes, the running characteristics are likely to vary, depending on whether the engine is operating or stopped. In such cases, the behavior of the running vehicle becomes contrary to the driver's intention, giving rise to a problem that the driver receives different feelings when operating the vehicle.